C# main method cannot run program - sum

Question

I am doing this C# code for my homework for calculating sum and substract
for the sum it is working fine, but I don't know how to code for two math equation as a code. I am thinking of the way I put the main method and brackets? There's only one error which what I have commented // on it.
Thank you in advance for your time.
using System;
namespace pg392mod
{
internal class Program
{
private static void Main(string[] args)
{
int firstNumber = 10;
int secondNumber = 2;
int result;
//2 call the method calculatesum and pass the 2 parameters to it
result = CalculateSum(firstNumber, secondNumber);
//3 write to console the result of the sum of the 2 numbers
Console.WriteLine("Sum of {0} and {1} is = {2}.", firstNumber, secondNumber, result);
Console.ReadLine();
}
public static int CalculateSum(int n1, int n2)
{
int sum;
sum = n1 + n2;
return sum;
}
//this is the error private static void Main(string[] args)
{
int firstNumber = 10;
int secondNumber = 2;
int result;
//2 call the method calculatesum and pass the 2 parameters to it
result = CalculateSum(firstNumber, secondNumber);
//3 write to console the result of the sum of the 2 numbers
Console.WriteLine("Substraction of {0} and {1} is = {2}.", firstNumber, secondNumber, result);
Console.ReadLine();
}
public static int CalculateSubstract(int n1,int n2)
{
int sub;
sub = n1 - n2;
return sub;
}
}
}

Answer 1

The error is thrown as you duplicated main definition. Items declared static must be unique as there is only one instance of them within the scope that they are declared.
Commenting out the line leaves you with a block of code, encompassed by { and } that is left floating and not within a defined scope.
The following would be better:
using System;
namespace pg392mod
{
internal class Program
{
private static void Main(string[] args)
{
int firstNumber = 10;
int secondNumber = 2;
int result;
//2 call the method calculatesum and pass the 2 parameters to it
result = CalculateSum(firstNumber, secondNumber);
//3 write to console the result of the sum of the 2 numbers
Console.WriteLine("Sum of {0} and {1} is = {2}.", firstNumber, secondNumber, result);
Console.ReadLine();
//2 call the method calculatesubtract and pass the 2 parameters to it
result = CalculateSubtract(firstNumber, secondNumber);
//3 write to console the result of the sum of the 2 numbers
Console.WriteLine("Substraction of {0} and {1} is = {2}.", firstNumber, secondNumber, result);
Console.ReadLine();
}
public static int CalculateSubtract(int n1,int n2)
{
int sub;
sub = n1 - n2;
return sub;
}
public static int CalculateSum(int n1, int n2)
{
int sum;
sum = n1 + n2;
return sum;
}
}
}